When light travels from one medium to another, some portion of the light is reflected from the interface between the two media. For example, typically about 4-5% of the light shining on a clear plastic substrate is reflected at the top surface.
Different approaches have been employed to reduce the reflection of polymeric materials. One approach is to use antireflective coatings such as multilayer reflective coatings consisting of transparent thin film structures with alternating layers of contrasting refractive index to reduce reflection. It is difficult, however, to achieve broadband antireflection using the multilayer antireflective coating technology.
Another approach involves using subwavelength surface structure (e.g., subwavelength scale surface gratings) for broadband antireflection. Methods for creating the subwavelength surface structure such as by lithography, tend to be relatively complicated and expensive. Additionally, it is challenging to obtain consistent low reflection broadband antireflection with minimized higher order diffraction from a roll-to-roll process with subwavelength scale surface gratings. A solution to provide high performance, low interference fringing, is desired, as is one also having relatively low reflection (i.e., average reflection over the visible range less than 0.5 percent), low birefringence (i.e., having an optical retardation value of less than 200 nm), and antireflective characteristics.